The purpose is to override *locally*:
- RTA_SRC ('from' option in ip-route)
- RTA_PREFSRC ('src' in ip-route)

For RTA_PREFSRC, there is a pull request that could replace this at
  https://github.com/jech/babeld/pull/18
But it looks better to do it our way.

TODO: documentation

To be pushed upstream.
Co-authored-by: Julien Muchembled <jm@nexedi.com>

TODO: documentation

To be pushed upstream.
Co-authored-by: Julien Muchembled <jm@nexedi.com>

Known issues:

  - we create a neighbour entry before the first successful challenge;
  - we compute HMAC for each HMAC TLV rather than just once;
  - we only support sending one HMAC TLV;
  - we don't support key rotation.
Co-authored-by: Clara Do <clarado_perso@yahoo.fr>
Co-authored-by: Weronika Kolodziejak <weronika.kolodziejak@gmail.com>

What was I thinking?

Since this causes flushbuf to take a struct interface, we're basically
carrying a struct interface all over the place.  Good.

Avoid the duplication by passing around an interface pointer.

src_plen for IPv4 routes imported from kernel has not been adjusted
to v4mapped encoding. Therefore IPv4 xroutes used an inconsistent encoding
which lead to failed comparisons when sending updates.

Routes received from neighbors with the same prefix as xroutes therefore
have been announced to neighbours instead.

This issue is fixed by converting src_plen on import.
Signed-off-by: Fabian Bläse <fabian@blaese.de>

This was introduced when the old_if table was made dynamic.

As pointed out by Toke Boot, this causes huge bursts of Hellos when we
encounter many new neighbours at a time.

Thanks to Dave Taht.

This removes an arbitrary limit on the number of interfaces.
Thanks to Christof Schulze.

This avoids a network meltdown in extreme cases.
Thanks to Teco Boot.

When adding a network interface that is already known to babeld, an
error message is displayed and the new configuration is ignored. This
message is adjusted to include the name of the interface being added so
it is visible from the logs without context

This removes a duplicate call to local_notify_interface(ifp, LOCAL_FLUSH)
which lead to duplicate output on the monitoring socket.

It was essentially a no-op with an inverted test.

This reverts commit 005f1197.

Thanks to Dave Taht for the report.

Now that we can carry more routes, try to carry them.

A late hello is an early warning sign of a cpu overload or
overbuffering.

Only set rp_filter to 0 if it contains a different value when
initializing new interfaces. This is helpful to run babeld inside docker
without --privileged